If $6a + 8b + 7c = -5$ and $x + 3y + 6z = -2$, what is $-24y + 32b - 8x - 48z + 28c + 24a$ ?
Explanation: $= 24a + 32b + 28c - 8x - 24y - 48z$ $= (4) \cdot (6a + 8b + 7c) + (-8) \cdot (x + 3y + 6z)$ $= (4) \cdot (-5) + (-8) \cdot (-2)$ $= -20 + 16$ $= -4$